With all the electronics aboard cruising boats today, the old magnetic compass must feel a bit ignored. Yet it is still one of the most reliable instruments on your boat, and will steer you home without electricity. With few moving parts, the compass is virtually maintenance free, but this old standby may still become damaged or show signs of age.
To get the longest life from your compass, keep it covered to protect it from the damaging sun. If the boat is stored in a cold climate, remove the compass from the boat and store it in a warm place. Even the best compass will eventually succumb if left exposed to the elements.
The most noticeable problem a compass may have is a crazed dome. Something dropped on a compass can crack the dome, but a plastic dome may become crazed if left exposed to the sun’s ultraviolet rays. Crazed or cracked domes or a failure of the seal between the dome and the compass body may cause a leak—a bubble in the compass is a sure sign of one.
“It makes economic sense to repair most compasses worth $150 or more or with a 3-inch or larger card,” says Steve Sprole, vice president of sales and marketing for Ritchie Navigation of Pembroke, Massachusetts. “We often get 20-year-old compasses sent to us for repair.”
Howard Maglathlin of Viking Instruments Inc. of Kingston, Massachusetts, agrees. ‘‘When we get a compass with a crazed dome and bubble we replace the dome, all the gaskets, and then clean and refill the compass,” he explains. “Generally you can expect to pay about 50 percent of what a new comparable compass would cost. For example, a 4- to 5-inch compass would cost between $175 and $300 dollars to refurbish, a 6-inch compass could run $300 or more.”
An old compass manufactured before the 1950s may be filled with a mixture of alcohol and water, but a modern one uses refined mineral spirits, referred to as compass oil. This fluid evaporates quickly and leaves no sign of a leak except a bubble. “You can add fluid to the compass but it’s a temporary fix,” Sprole explains. “Over time, especially if it’s cold, the bubble will return.”
Most compasses develop this bubble during winter storage because the cold temperature causes the fluid to contract, pulling air into the compass. In very hot weather the fluid expands, creating pressure in the compass, forcing the fluid to leak out. When the fluid cools down, it contracts and air is drawn back into the compass. While a compass has a bellows designed to compensate for fluid expansion or contraction, it won’t stop a leak.
You can put off an inevitable repair by refilling the compass yourself. Compass oil can be purchased from most compass repair facilities, marine retailers, or online. To make filling the compass easier, you need a very small funnel or purchase one of the large syringes designed to inject epoxy, such as the West System. The point of this type of syringe easily fits into the fill hole in the side of the compass.
Slowly rotate the compass until the filling screw is facing up. Loosen this screw and remove it. Add fluid until full, and then rock the compass back and forth to allow all the air to get out. You may have to add more oil as the bubbles work their way out. Replace the screw and turn the compass upright. If you still see a small bubble, repeat the process.
Another point of wear is the pivot that the compass card turns on. Even though this pivot is made from hardened steel resting on a jewel bearing, engine vibration and constant boat movement can eventually cause wear. As the pivot wears, the compass card becomes less sensitive, and a severely worn pivot may cause the compass card to become erratic and jerky as it turns. This happens gradually so it’s less noticeable than a bubble.
The easiest test for this problem is to tie the boat against a dock so it maintains the same compass heading. Then place a metal object like a large wrench next to the compass and watch the card move. Remove the wrench and the card should smoothly swing back to the heading it was on. Place the wrench on the other side of the compass and repeat the test. If the card does not return to the exact heading, then the pivot may be worn. Try this test when the boat is tied up on different headings. If the card is worn it should be repaired by a professional compass repair shop.
If you can’t deliver the compass to a repair shop you can mail it in for servicing. Jeff Kaufmann of Cape Compass, in West Falmouth, Massachusetts, says, “Just be sure to place a leaking compass in a plastic bag because the Post Office doesn’t like to get soggy packages.” He also says to contact the repair facility and get specific shipping instructions and double box the compass since it is heavy and can migrate to the side of the box, particularly if only Styrofoam peanuts are used. Kaufmann also cautions, “American compasses can be mailed without a problem, but the German Plath compass requires special handling.”
Kaufmann adds, “Another point to consider when deciding whether to repair a compass or replace it is the money you have invested in having your compass adjusted. I travel the East Coast adjusting compasses, and this can run into several hundred dollars or more for a larger boat. If you purchase a new compass you have to have it adjusted, but if you tell the repair facility you want to maintain the adjustment, they won’t change the compensating magnets when they test the compass.”
I nursed my 5-inch compass along for five years, burping it in the spring after the bubble kept reappearing following a winter layup. I didn’t have this problem when the boat was south for the winter, but eventually the dome became crazed, so I had to admit defeat and send it to be rebuilt. I now have a like-new compass with a crystal clear dome and no bubble. So I would recommend you bite the bullet and have your compass serviced, if, after you refill it, a bubble reappears.